How do chemists find the composition of unknown samples?

Flame tests-method 1 for cations

1. Dip damp wooden splint into sample of metal

2. Place sample into blue Bunsen flame.

3. Record the colour of the flame.

Lithium ions (flame test)

Crimson flame

Sodium ions(flame test)

Yellow flame

Potassium ions (flame test)

Lilac flame

Copper(III) ions flame test

Green flame

Calcium ions (flame test)

Orange-red flame

Test for aqueous cations

Add a few drops of dilute sodium hydroxide

If you get a coloured insoluble hydroxide, metal was in a compound

Calcium ions from NaOH

White precipitate

Copper(II) from NaOH

Blue precipitate

Iron(II) from NAOH

Green precipitate

Iron(III) from NAOH

Orange brown precipitate

Zinc from NAOH

White precipitate and precipitate re dissolves

Test for Carbonate ions

React substance with HCL

Gas can be bubbled through limewater, if cloudy then the gas is co2

A chemical reaction is taking place in a test tube. What methods could be used to collect the gas?

Attach the top of the test tube to a gas syringe 

Place an upside down measuring cylinder over the test tube to trap the gas

Halides test

Add dilute nitric acid to remove carbonate or sulfate ions

then add silver nitrate solution

the colour of the solution will depend on what precipitate forms

silver chloride result in halide test

White precipitate

silver bromide result in halide test

Cream precipitate

silver iodide result in halide test

Yellow precipitate

Sulfates test

First add dilute hydrochloric acid to remove carbonate ions

then add barium chloride solution containing barium ions

A white precipitate will form when sulfate ions are present

Spectrascope

Detects wavelength of light and gives line soectrum

Adv of spectroscope

Sensitive

Accurate

Fast